#include<iostream>
using namespace std;
int main(){
    int n;
    cin>>n;
    if(n>=90&&n<=100)cout<<"A"<<endl;
    else if(n>=80&&n<=89)cout<<"B"<<endl;
    else if(n>=70&&n<=79)cout<<"C"<<endl;
    else if(n>=60&&n<=69)cout<<"D"<<endl;
    else if(n>=0&&n<=59)cout<<"E"<<endl;
    else cout<<"F"<<endl;
    return 0;
}
